Vaccine side effects don’t tell you how strong your immune system is

If somebody will get a headache or feels a bit below the climate after receiving a COVID-19 vaccine, it’s develop into frequent to listen to them say one thing like “Oh, it simply means my immune system is actually working onerous.” On the flip side, when individuals don’t discover any side effects, they generally fear the shot isn’t doing its job or their immune system isn’t reacting in any respect.

Is there any hyperlink between what you can notice after a vaccine and what’s occurring on the mobile degree inside your physique? Robert Finberg is a doctor who makes a speciality of infectious ailments and immunology on the Medical College on the College of Massachusetts. He explains how this notion doesn’t match the fact of how vaccines work.

What does your physique do when you get a vaccine?

Your immune system responds to the overseas molecules that make up any vaccine by way of two totally different programs.

The preliminary response is attributable to what’s referred to as the innate immune response. This system is activated as quickly as your cells discover you’ve been uncovered to any overseas materials, from a splinter to a virus. Its aim is to get rid of the invader. White blood cells referred to as neutrophils and macrophages journey to the intruder and work to destroy it.

This primary line of protection is comparatively short-lived, lasting hours or days.

The second line of protection takes days to weeks to stand up and operating. This is the long-lasting adaptive immune response. It relies on your immune system’s T and B cells that study to acknowledge specific invaders, reminiscent of a protein from the coronavirus. If the invader is encountered once more, months and even years sooner or later, it’s these immune cells that may acknowledge the outdated enemy and begin producing the antibodies that may take it down.

Within the case of the SARS-CoV-2 vaccines, it takes roughly two weeks to develop the adaptive response that brings long-lasting safety towards the virus.

When you get the vaccine shot, what you’re noticing within the first day or two is a part of the innate immune response: your physique’s inflammatory response, geared toward shortly clearing the overseas molecules that breached your physique’s perimeter.


It varies from individual to individual, however how dramatic the preliminary response is doesn’t essentially relate to the long-term response. Within the case of the 2 mRNA COVID-19 vaccines, well over 90% of people immunized developed the protective adaptive immune response whereas fewer than 50% developed any side effects, and most had been delicate.

You might by no means know how strongly your physique’s adaptive immune response is gearing up.

The underside line is you can’t gauge how properly the vaccine is working inside your physique based mostly on what you can detect from the skin. Completely different individuals do mount stronger or weaker immune responses to a vaccine, however post-shot side effects gained’t tell you which you are. It’s the second, adaptive immune response that helps your body gain vaccine immunity, not the inflammatory response that triggers these early aches and pains.

What are side effects, anyway?

Side effects are regular responses to the injection of a overseas substance. They embody issues like fever, muscle ache and discomfort on the injection web site, and are mediated by the innate immune response.

Neutrophils or macrophages in your physique discover the vaccine molecules and produce cytokines—molecular alerts that trigger fever, chills, fatigue and muscle ache. Docs count on this cytokine response to occur any time a overseas substance is injected into the physique.

In research the place neither recipients nor researchers knew which people had been getting the mRNA vaccine or a placebo, roughly half of people aged 16 to 55 who received a SARS-CoV-2 vaccine developed a headache after the second dose. This response might relate to the vaccine—however 1 / 4 of people that acquired only a placebo additionally developed a headache. So within the case of quite common signs, it may be fairly tough to attribute them to the vaccine with any certainty.

Researchers anticipate some experiences of side effects. Adverse events, however, are issues that physicians don’t count on to occur on account of the vaccine. They would come with organ failure or severe harm to any a part of the physique.

The blood clots that triggered the U.S. to pause distribution of the Johnson & Johnson vaccine are a really uncommon occasion, apparently occurring with one-in-a-million frequency. Whether or not they’re undoubtedly brought on by the vaccine is nonetheless below investigation – but when scientists conclude they’re, blood clots could be a particularly uncommon side impact.

What element within the shot causes side effects?

The one “energetic ingredient” in the Pfizer and Moderna vaccines is the mRNA instructions that tell the recipient’s cells to construct a viral protein. However the pictures produce other parts that assist the mRNA journey inside your physique.

To get the vaccine’s mRNA into the vaccinated particular person’s cells the place it could do its job, it should evade enzymes within the physique that might naturally destroy it. Researchers protected the mRNA within the vaccine by wrapping it in a bubble of lipids that assist it keep away from destruction. Different substances within the pictures – like polyethylene glycol, which is a part of this lipid envelope – may trigger allergic responses.

If I really feel sick after my shot, does that sign strong immunity?

Scientists haven’t recognized any relationship between the preliminary inflammatory response and the long-term response that results in safety. There’s no scientific proof that somebody with extra apparent side effects from the vaccine is then higher shielded from COVID-19. And there’s no cause that having an exaggerated innate response would make your adaptive response any higher.


Both the authorized mRNA vaccines supplied protecting immunity to over 90% of recipients, however fewer than 50% reported any response to the vaccine and much fewer had extreme reactions.